Air-cooled grate block

ABSTRACT

An air-cooled grate block of a grate for the thermal treatment of waste, in which the grate blocks are arranged so as to rest one on top of the other in a step-like manner. The block body designed as a cast part has a top wall, forming a bearing surface, and a front wall, on which a foot is integrally formed. A first cooling passage section runs from a wall inlet, arranged on the underside of the top wall, through the top wall and the front wall to an outlet opening arranged in the front wall. A cooling passage wall which starts from an inlet opening arranged adjacent to the foot and to the front wall and is at a distance from the front wall and the top wall forms a second cooling passage section fluidically connected to the first cooling passage section at the wall inlet. A grate which consists of the abovementioned grate blocks is likewise described.

The present invention relates to a grate block as part of a grate for aplant for the thermal treatment of waste.

The heart of a waste material incineration plant is the incinerationgrate. Here, the waste materials, for example household garbage, isconveyed from one end of the incineration grate to the other end of theincineration grate. The oxygen required for the combustion of the wastematerials is present in the air in sufficient quantity. In the process,the air, also called primary air, is forced from below through theincineration grate and is thus fed to the combustion space containingthe waste materials to be incinerated.

One type of the various known incineration grate types is the “stepgrate”. Such a step grate comprises grate blocks which are arranged sideby side and are fixedly connected and which form the individual grateblock rows. The grate block rows following one another are offset fromone another in a step-like manner and rest one on top of the other withthe front walls, facing the combustion space, of the grate blocks whichform the grate block rows. Some of the grate block rows are arranged tobe movable, for example every second grate block row. The waste materialis conveyed onto the grate block row following in the transportdirection by the lifting movement of these movably arranged grate blockrows.

The waste materials which are incinerated in the abovementionedincineration plant vary widely in nature. The range extends fromhousehold garbage to industrial waste and actual fuels, e.g. wood in theform of sawdust, biomass and suchlike. Of course, the calorific value ofthese waste materials varies greatly, depending on the type of wastematerial. However, there are also considerable variations with regard tothe calorific value within one type of waste material. Theseconsiderable variations in the calorific value also result inconsiderable variations in the thermal and mechanical loading of theincineration grate, for example of the individual grate blocks.

At average calorific values (up to about 10 MJ/kg), the incinerationgrates or the individual grate blocks can be adequately cooled with air(primary air). For waste materials having a higher calorific value,incineration grates having water-cooled grate blocks are known from theprior art. Adequate cooling of the grate blocks is very important, sincethere is otherwise the risk of melting of the incineration grate.

EP 1 191 282 describes a grate block which has a cooling space for wateron its bottom side facing away from the combustion space.

EP 1 219 898 discloses a grate block having a cooling element attachedbelow the bearing surface for the waste. Water is also used here for thecooling.

DE 10 2004 032 291 discloses an air-cooled grate plate having a flowpassage formed below the top side of the grate plate.

Although water-cooled grate blocks provide a means which enablesefficiently cooled incineration grates to be produced, such incinerationgrates have the disadvantage that both the production thereof and thesubsequent process are much more costly than in the case of incinerationgrates which are composed of air-cooled grate blocks.

The object of the present invention is to provide a grate block whichhas at least equally good wear resistance and thus an equally longservice life compared with a water-cooled grate block and which at thesame time avoids the disadvantages of the latter with regard to the highcost in terms of production and process.

The object is achieved by a grate block having the features ofindependent claim 1. Preferred embodiments are the subject matter of thedependent claims.

The grate block according to the invention has the features according toclaim 1. The grate block has a block body which is designed as a castpart. The block body has a top wall, which forms a bearing surface, anda front wall, on which a foot is integrally formed. The grate block ispart of a grate for the thermal treatment of waste. In this case, thegrate blocks are arranged one above the other in a step-like manner andthe individual grate blocks rest with the foot integrally formed on thefront wall on the bearing surface formed by the top wall of thefollowing grate block (step grate). The waste to be thermally treatedlikewise rests on this bearing surface formed by the top wall. The gratecan have an inclination. This inclination is within a range of 0° to26°, preferably within the range of 10° to 18°, relative to an imaginaryhorizontal plane. A wall inlet is arranged on the underside of the topwall. This wall inlet lies on that side of the top wall which faces awayfrom the combustion space. Starting from the wall inlet, a first coolingpassage section runs through the top wall and the front wall to anoutlet opening arranged in the front wall. An inlet opening is arrangedadjacent to the front wall and to the foot integrally formed thereon. Acooling passage wall which is at a distance from the front wall and thetop wall starts from the inlet opening and forms a second coolingpassage section fluidically connected to the first cooling passagesection at the wall inlet.

The first cooling passage section and the second cooling passage sectiontogether form a cooling passage which has a substantially S-shapedcourse in longitudinal section. The cross section or the cross-sectionalarea of the first cooling passage section and of the second coolingpassage section—and thus of the substantially S-shaped coolingpassage—is constant in the simplest embodiment. However, the crosssection may also vary.

The grate block according to the invention permits the use of gaseouscooling media, in particular air, even during the thermal treatment ofwaste materials having a higher calorific value (>10 MJ/kg). Watercooling, which is often required in the case of waste materials having ahigher calorific value, is dispensed with. The grate block according tothe invention permits excellent and differentiated cooling of thosepoints of the grate block which are subjected to the greatest thermalloading. This is therefore very advantageous since—in the case of aircooling—the primary air available for the cooling is limited.Furthermore, the primary air used for the cooling is heated by about120° to 150°, for which reason preheating (hitherto necessary) of theprimary air can be dispensed with. In addition to the omission of thepreheating of the primary air, even cooler air than was hithertopossible can be used for the cooling. The cooling is thus additionallyimproved overall. The grate block according to the invention achievesoutstanding, i.e. long, service life comparable with the service life ofwater-cooled grate blocks.

In a preferred embodiment, the first cooling passage section and thesecond cooling passage section run with a varying cross section. Theterm “cross section” designates the cross-sectional area of the firstand the second cooling passage sections. The shape of thecross-sectional area may vary. Possible cross-sectional shapes arerectangular, quadrilateral, polygonal, e.g. a truncated hexagon,circular or oval.

The heat removal by the gaseous cooling medium, preferably the primaryair, designates the quantity of heat dissipated by the cooling mediumper unit time. The heat removal depends, inter alia, on the flowvelocity of the cooling medium relative to its surroundings, in thepresent case the first and the second cooling passage sections. It isall the greater, the higher the flow velocity of the cooling medium is.

If the cross section of the two cooling passage sections varies, thismeans that the cross-sectional area changes. The cross-sectional areacan become smaller or larger. If the cross-sectional area becomessmaller for example, the flow velocity of a gaseous cooling medium,preferably of the cooling air, increases, which leads to greater coolingas a result of the increased heat removal by the gaseous cooling medium.Increased heat removal means that the gaseous cooling medium absorbs agreater heat quantity from its surroundings and dissipates said heatquantity due to the increased flow velocity on account of the reducedcross-sectional area. With a corresponding variation of the crosssection of the first and the second cooling passage sections, highlydifferentiated cooling of individual regions of the grate block isachieved. As a result, the cooling can be adapted to the specificthermal loading of the individual grate block region. Thus, for example,the front wall of the grate block can be cooled to a deliberatelyincreased extent.

Widening the cross section of the first cooling passage section or ofthe second cooling passage section in regions which are thermally loadedto a less pronounced extent reduces the flow velocity of the gaseouscooling medium, e.g. of the primary air, and thus also reduces the heatremoval achieved. It thus becomes possible, with a limited quantity ofcooling medium, e.g. primary air, to also cool regions of the grateblock that are thermally loaded to a less pronounced extent, whereby thecooling overall is improved.

In another embodiment, the grate block has a rib extending in thelongitudinal direction of the block body. The rib is integrally formedon the top wall and the front wall and is arranged substantiallyperpendicularly thereto. The stability of the grate block is increasedby means of the rib.

In a preferred embodiment, the rib is a central rib, i.e. it is arrangedcentrally in the transverse direction of the block body. The arrangementof the rib in the center additionally simplifies the production of thegrate blocks according to the invention by casting, since identical halfshells can be used.

In a preferred embodiment, the first cooling passage section and thesecond cooling passage section fluidically connected thereto extend overthe entire length of the top wall of the grate block according to theinvention. Cooling of the grate block over the entire length of the topwall is thus achieved.

However, it is also possible according to a further embodiment for thefirst cooling passage section and the second cooling passage section toextend only over part of the length of the top wall. The first coolingpassage section and the second cooling passage section preferably extendover 10%-90%, in particular preferably over 30%-70%, of the length ofthe top wall of the grate block.

In a further embodiment of the grate block according to the invention,the cross section of the second cooling passage section increases fromthe inlet opening toward the wall inlet. The cross section of the firstcooling passage section, on the other hand, decreases from the wallinlet toward the outlet opening. The cross-sectional change can beeffected both continuously and in discrete steps. A continuouscross-sectional change is obtained, for example, if the first and/or thesecond cooling passage section has a conical section. Due to the changein the cross section of the first cooling passage section and of thesecond cooling passage section, zones cooled to a different extent areobtained in the first cooling passage section and in the second coolingpassage section. In this case, the cooling is weaker in zones having agreater cross section and stronger in zones having a smaller crosssection.

In another embodiment, the grate block has deflecting webs integrallyformed on the rib, preferably a central rib, and projectingsubstantially perpendicularly from the latter. These deflecting webs arearranged offset from one another.

In a further embodiment, the deflecting webs form a meandering passagewhich is fluidically connected to the second cooling passage section atthe inlet opening. In this case, a passage inlet opening is in aposition which is dependent on a position of the grate block relative toa grate block following in a direction L.

The direction L corresponds to the conveying direction of the waste inthe longitudinal direction of the grate. In the process, the wastepasses through various zones, starting with the drying zone at an end ofthe grate right through the combustion zone to the burnout zone at theother end, opposite the drying zone, of the grate.

In a preferred embodiment, the top wall of the grate has trough-shapedrecesses on its side facing the combustion space.

The trough-shaped recesses are located in a region of the top wall whichadjoins the front wall of the grate block. Waste or slack restscontinuously in this region during the operation of the grate, whichmeans pronounced thermal loading.

Incinerated waste or slag collects in these trough-shaped recessesduring operation of the incineration grate. The incinerated waste or theslag form an insulating layer between the top wall and the combustionspace and thus reduce the input of heat from the combustion space intothe grate block.

The grate blocks according to the invention can be used in a grate. Sucha grate preferably comprises only grate blocks according to theinvention.

A grate has, as a rule, a plurality of fixed grate block rows and aplurality of movable grate block rows. These grate block rows are formedby a plurality of grate blocks arranged side by side and attached to ablock-retaining tube, the grate blocks arranged next to one anotherbeing fixedly connected to one another. The fixed and the movable grateblock rows are arranged alternately and in a step-like manner. In thiscase, both the fixed and the movable grate block rows are formed bygrate blocks according to the invention.

Whereas the block-retaining tubes of fixed grate block rows are attachedto fixed brackets, block-retaining tubes of movable grate block rows areassigned to movable grate carriages. These grate carriages are driven,for example, by means of hydraulic cylinders and in the process aremoved forward and backward via rollers. As a result, the movable grateblock rows are likewise moved and thus exert a pushing and shearingeffect on the waste resting on the grate. The waste is thus firstlycirculated, wherein new waste portions are constantly subjected to thethermal treatment in the combustion space. Secondly, constant forwardconveyance of the waste in the direction of a grate end is thusachieved.

The grate block according to the invention is explained in more detailbelow with reference to exemplary embodiments shown in the drawings, inwhich, purely schematically:

FIG. 1 shows a first embodiment of the grate block in longitudinalsection;

FIG. 2 shows a further embodiment of the grate block in longitudinalsection;

FIG. 3 shows a further embodiment of the grate block in longitudinalsection, having an extended top wall;

FIG. 4 shows a further embodiment of the grate block in longitudinalsection, having a substantially S-shaped cooling passage of mean lengthwith respect to the distance from the front to the rear wall;

FIG. 5 shows a further embodiment of the grate block in longitudinalsection, having a short, substantially S-shaped cooling passage;

FIG. 6 shows a further embodiment of the grate block in longitudinalsection, having a short, substantially S-shaped cooling passage andadditional deflecting webs arranged offset;

FIG. 7 shows an embodiment of the grate block in cross section;

FIG. 8 shows a further embodiment of the grate block in cross section;

FIG. 9 shows a further embodiment of the grate block in cross section,having a trough-shaped recess on that side of the top wall which facesthe combustion space;

FIG. 10 shows three grate blocks arranged side by side according to FIG.7, in cross section;

FIG. 11 shows three grate blocks arranged side by side according to FIG.8, in cross section;

FIG. 12 shows three grate blocks arranged side by side according to FIG.9, in cross section;

FIG. 13 a shows four grate blocks, arranged one above the other in astep-like manner, according to the embodiment shown in FIG. 6, themovably arranged grate blocks being fully extended;

FIG. 13 b shows four grate blocks, arranged one above the other in astep-like manner, according to the embodiment shown in FIG. 6, themovably arranged grate blocks being arranged in a central position;

FIG. 13 c shows four grate blocks, arranged one above the other in astep-like manner, according to the embodiment shown in FIG. 6, themovably arranged grate blocks being fully retracted;

FIG. 14 a shows four grate blocks, arranged side by side, in aperspective view according to the embodiment shown in FIG. 9, havingtrough-shaped recesses;

FIG. 14 b shows in an enlarged detail one of the trough-shaped recessesaccording to FIG. 14 a; and

FIG. 15 shows a detail of a step grate having fixed and movably arrangedgrate blocks.

FIG. 1 shows a grate block according to the invention having a blockbody 5 which is designed as a cast part. The block body 5 has a top wall10, which forms a bearing surface 15, and a front wall 20. A foot 25 isintegrally formed on the front wall 20. The foot 25 is intended to reston the bearing surface 15 of a following grate block 1 in a relativelydisplaceable manner. Arranged on the underside 30 of the top wall 10,that is to say on the side facing away from the combustion space 2, is awall inlet 35, from which a first cooling passage section 40 runsthrough the top wall 10 and the front wall 20 to an outlet opening 45arranged in the front wall 20. In the embodiment shown, the outletopening 45 is directed obliquely downward, i.e. in the direction of thebearing surface 15 of the following grate block 1. Arranged adjacent tothe foot 25 and to the front wall 20 is an inlet opening 50, startingfrom which a cooling passage wall 55 which is at a distance from thefront wall 20 and the top wall 10 forms a second cooling passage section60 fluidically connected to the first cooling passage section 40 at thewall inlet 35. In the embodiment shown, the first and the second coolingpassage sections 40, 60 do not extend over the entire length of the topwall 10. The cross section or the cross-sectional area of the firstcooling passage section 40 and of the second cooling passage section 60shown in FIG. 1 varies in the course of the two cooling passagesections. However, the cross section can also be kept constant.

The grate block according to the invention has, for example, thefollowing dimensions: a length of 500 mm to 700 mm, a height ofapproximately 150 mm and a width of approximately 100 mm.

FIG. 2 shows a further embodiment of the grate block according to theinvention. In this embodiment, the grate block has a rib 65 and a rearwall 75. The rib 65 is integrally formed on the front wall 20, the topwall 10, the cooling passage wall and the rear wall 75 and is arrangedsubstantially perpendicularly thereto. The rib 65 extends from the frontwall 20 up to the rear wall 75. The rear wall 75 is provided with a hook80. The grate block 1 is attached to a block-retaining tube (not shownhere) by means of this hook 80. The circumference of the grate block 1is not exactly rectangular. On the contrary, said grate block 1 issloped where the top wall 10 meets the front wall 20.

FIG. 3 shows a further, modified embodiment of the grate block 1according to the invention. At the circumference, the top wall 10 andthe front wall 20 again have a slope, which is extended by a lug 85beyond the outer side 21, facing the combustion space 2, of the frontwall 20. The lug 85 therefore projects beyond the outer side 21 of thefront wall 20. The outlet opening 45 thus points substantiallyperpendicular downward in the direction of the bearing surface 15 of afollowing grate block 1.

FIG. 4 shows another embodiment of a grate block 1 having a block body5. The block body 5 has a front wall 20, a top wall 10 and a rear wall75. A foot 25 is integrally formed on the front wall 20 and a hook 80 isintegrally formed on the rear wall 75. A first cooling passage section40 runs from a wall inlet 35 through the top wall 10 and the front wall20 to an outlet opening 45. Extending from an inlet opening 50, which isarranged adjacent to the foot 25 and to the front wall 20, is a coolingpassage wall 55 which is at a distance from the front wall 20 and thetop wall 10 and which forms a second cooling passage section 60fluidically connected to the first cooling passage section 40 at thewall inlet 35. The first and the second cooling passage sections 40, 60extend only over part of the length of the top wall 10. In theembodiment shown, they extend approximately over half the length of thetop wall 10 and thus over a region subjected to greater thermal loading.

FIG. 5 shows an embodiment of a grate block according to the inventionsimilar to the embodiment shown in FIG. 4. In this case, the firstcooling passage section 40 and the second cooling passage section 60extend only over a region of approximately one third of the length ofthe top wall 10, said region adjoining the front wall 20.

FIG. 6 shows another embodiment of a grate block 1 according to theinvention. The grate block 5, designed as a cast part, has a top wall10, which forms a bearing surface 15, and a front wall 20, wherein afoot 25 is integrally formed on the front wall 20. The foot 25 isintended to rest on the bearing surface 15 of a following grate block 1in a relatively displaceable manner. Arranged on the underside 30 of thetop wall 10, on the side facing away from the combustion space 2, is awall inlet 35, from which a first cooling passage section 40 runsthrough the top wall 10 and the front wall 20 to an outlet opening 45arranged in the front wall 20. In the embodiment shown, the outletopening 45 is directed obliquely downward, i.e. in the direction of thebearing surface 15 of the following grate block 1. Arranged adjacent tothe foot 25 and to the front wall 20 is an inlet opening 50, startingfrom which a cooling passage wall 55 at a distance from the front wall20 and the top wall 10 forms a second cooling passage section 60fluidically connected to the first cooling passage section 40 at thewall inlet 35. In the embodiment shown, the first and the second coolingpassage sections 40, 60 extend only over approximately the front thirdof the length of the top wall 10. The cross section or thecross-sectional area of the first cooling passage section 40 and of thesecond cooling passage section 60 shown in FIG. 6 varies in the courseof the two cooling passage sections. Starting from the inlet opening 50,the second cooling passage 60 has a narrow cross section along the frontwall 20, said cross section then widening considerably toward the wallinlet 35. In the first cooling passage section 40, the widened crosssection narrows again toward the outlet opening 45 to approximately thesame narrow cross section as runs in the second cooling passage 60 alongthe front wall. In addition, the block body 5 has a rib 65 which isintegrally formed on the front side 20, the top side 10 and a rear side75 and is arranged substantially perpendicularly thereto. In thisembodiment, too, the rear wall 75 is provided with a hook 80. Integrallyformed on the rib 65 is a deflecting web 70 which is arrangedsubstantially perpendicularly to the rib 65.

In the embodiment shown, there are a total of 5 deflecting ribs 70,which run obliquely downward from the top in a direction L. Thedirection L also corresponds to the conveying direction of the waste(not shown) resting on the bearing surface 15. The deflecting webs 70are alternately arranged offset. That is to say, the deflecting webs 70are either integrally formed with their top end on the underside 30 ofthe top wall 10 or are spaced apart with their top end from the bottomside 30 of the top wall 10 in such a way that the bottom end 72 of thedeflecting webs 70 is located in a plane with the bottom surface 26 ofthe foot 25.

FIG. 7 shows a cross section through a grate block 1 according to theinvention. The block body 5 has a top wall 10 having a bearing surface15 and an underside 30 and a rib 65. A first cooling passage section 40runs through the top wall 10. The cooling passage wall 55 at a distancefrom the top wall 10 forms together with the latter a second coolingpassage section 60. The rib 65 is arranged centrally in the embodimentshown.

FIG. 8 shows a further cross section through a grate block 1. Here, ofthe block body 5, only the top wall 10 having the cooling passagesection 40, which runs through the top wall 10 and which, as can be seenhere in cross section, is divided into 4 smaller cooling passagesections, and the cooling passage wall 55, at a distance from the topwall 10, and the second cooling passage section 60 can be seen. Likewiseshown is the rib 65, which again is arranged in the center of the blockbody 5 and substantially perpendicularly thereto.

FIG. 9 shows another embodiment of a grate block 1 according to thepresent invention. The block body 5 again has a top wall 10, forming abearing surface 15 and having an underside 30, a cooling passage wall 55at a distance from the top wall 10, and a centrally arranged rib 65. Thefirst cooling passage section 40 running through the top wall 10 and thesecond cooling passage section 60 formed by the cooling passage wall 55and the top wall 10 can likewise be seen. In addition, the top wall hasa trough-shaped recess 90. As can be seen from FIG. 14 a, this recess 90extends only over approximately the front third of the grate block 1.Slag collects in this trough-shaped recess, which results in screeningof the grate block relative to the combustion space 2. The thermalloading of the grate block 1 is lower in this region of the screeningdue to a reduced input of heat.

FIG. 10, with three grate blocks 1 according to FIG. 7 which arearranged side by side, shows a detail of a grate block row in crosssection. In this case, the first cooling passage section 40 and thesecond cooling passage section 60 are jointly formed by in each case twoadjacently arranged grate blocks 1. Whereas the first cooling passagesection 40 runs through the top wall 10, the second cooling passagesection 60 is formed by the cooling passage wall 55, which is arrangedat a distance from the top wall 10, together with this top wall 10. Thelateral boundary of both the first cooling passage section 40 and thesecond cooling passage section 60 is formed by the ribs 65 of twoadjacently arranged grate blocks 1, said ribs 65 being arrangedsubstantially centrally with respect to the individual grate block.

FIG. 11, with three grate blocks 1 according to FIG. 8 which arearranged side by side, shows a detail of a grate block row in crosssection. Of the block body 5 of each of the three grate blocks 1 shown,the top wall 10, the cooling passage wall 55 at a distance therefrom andthe rib 65, again arranged substantially centrally, can be seen. Thefirst cooling passage section 40 runs through the top wall 10. Thedivision of the first cooling passage section into 4 smaller coolingpassage sections can likewise again be seen, said cooling passagesections running through the top wall 10 and through the front wall 20and opening into the outlet openings arranged in this front wall 20. Thesecond cooling passage 60 is jointly formed by two adjacent grate blocks1.

FIG. 12, with three grate blocks 1 according to FIG. 9 which arearranged side by side, shows a detail of a grate block row in crosssection. The first cooling passage section 40 and the second coolingpassage section 60 are jointly formed by in each case two adjacentlyarranged block bodies 5 of the grate blocks 1. Whereas the first coolingpassage section 40 runs through the top wall 10, the second coolingpassage section 60 is formed by the cooling passage wall 55, which isarranged at a distance from the top wall 10, and this top wall 10. Thelateral boundary of both the first cooling passage section 40 and thesecond cooling passage section 60 is formed by the ribs 65 of twoadjacently arranged grate blocks 1, said ribs 65 being arrangedsubstantially centrally with respect to the individual grate block. Thetrough-shaped recess 90 in the top wall 10 of the block bodies 5 canlikewise be seen.

FIGS. 13 a, 13 b, 13 c each show, in cross section, four grate blockrows 100, 101, 102 and 103 which are arranged one behind the other in astep-like manner and which each comprise a plurality of grate blocks 1arranged side by side. The embodiment of the grate blocks 1 showncorresponds to that of FIG. 6. The grate block rows 100 and 102 arefixed grate block rows, whereas the grate block rows 101 and 103 arearranged to be movable. The grate blocks 1 of the movable grate blockrows 101 and 103 can be seen in different positions in FIGS. 13 a, 13 band 13 c. In FIG. 13 a, the grate blocks 1 of the movable grate blockrows 101 and 103 are fully extended in direction L, which corresponds tothe conveying direction of the waste. In this case, a meandering passage110 having a passage inlet opening 115 is formed by the deflecting webs70 of the grate blocks 1 of the movable grate block rows 101 and 103,and the gaseous cooling medium, e.g. the primary air, flows through saidmeandering passage 110. In FIG. 13 b, the grate blocks 1 of the movablegrate block rows 101 and 103 are shown, in direction L, in a centralposition, which is located between the fully extended position shown inFIG. 13 a and the fully retracted position, in the opposite direction todirection L, shown in FIG. 13 c. As a result, both the length of themeandering passage 110 and the position of the passage inlet opening 115change. The result of this is that the grate blocks 1 of the movablegrate block row 101 and 103 are always cooled in that region which isexposed to the waste in the combustion space 2.

FIG. 14 a shows a perspective view of a grate block row consisting offour grate blocks 1 arranged side by side. The top wall 10, forming abearing surface 15, the front wall 20 and the foot 25 integrally formedthereon can be seen here. The rear wall 75 provided with a hook 80 andthe rib 65 arranged centrally with respect to the individual grate block1 are likewise shown. Only partly visible is the cooling passage wall55, which, starting from an inlet opening 50, runs at a distance fromthe front wall 20 and the top wall 10 toward a wall inlet 35 and forms asecond cooling passage section 60 which is fluidically connected to thefirst cooling passage section 40 at the wall inlet 35. The first coolingpassage section 40 runs from the wall inlet 10 through the top wall 10and the front wall 20 toward outlet openings 45. In the embodimentshown, the block body 5 has trough-shaped recesses 90 in the top wall10. These trough-shaped recesses 90 are arranged in the top wall 10 inthat region of the grate block 1 which adjoins the front wall 20. Thisregion is continuously exposed to the waste during operation.

FIG. 14 b shows, in an enlarged detail of FIG. 14 a, the trough-shapedrecesses 90 arranged in the top wall 10.

FIG. 15 shows a longitudinal section of an incineration grate havinggrate blocks 1 arranged one behind the other in a step-like manner, asknown from the prior art. The grate blocks 1 are not arrangedhorizontally but rather rise obliquely upward in direction L.

1. An air-cooled grate block of a grate for the thermal treatment ofwaste, in which the grate blocks are arranged so as to rest one on topof the other in a step-like manner, comprising a block body, which isdesigned as a cast part and which has a top wall, forming a bearingsurface, and a front wall, on which a foot is integrally formed, a firstcooling passage section running from a wall inlet, arranged on anunderside of the top wall, through the top wall and the front wall to anoutlet opening arranged in the front wall, wherein a cooling passagewall which starts from an inlet opening arranged adjacent to the footand to the front wall and is at a distance from the front wall and thetop wall forms a second cooling passage section fluidically connected tothe first cooling passage section at the wall inlet.
 2. The grate blockas claimed in claim 1, wherein the first cooling passage section and thesecond cooling passage section run with a varying cross section.
 3. Thegrate block as claimed in claim 1, wherein the grate block has a ribwhich extends in the longitudinal direction of the block body, isintegrally formed on the top wall and the front wall and is arrangedsubstantially perpendicularly thereto.
 4. The grate block as claimed inclaim 3, wherein the rib is a central rib.
 5. The grate block as claimedin claim 1, wherein the first cooling passage section and the secondcooling passage section extend over the entire length of the top wall.6. The grate block as claimed in claim 1, wherein the first coolingpassage section and the second cooling passage section extend only overthe part of the length of the top wall.
 7. The grate block as claimed inclaim 1, wherein the cross section of the second cooling passage sectionincreases from the inlet opening toward the wall inlet and the crosssection of the first cooling passage section decreases from the wallinlet toward the outlet opening.
 8. The grate block as claimed in claim3, wherein the block body has deflecting webs integrally formed on therib and projecting substantially perpendicularly from the latter, thedeflecting webs being arranged offset from one another.
 9. The grateblock as claimed in claim 8, wherein the deflect webs form a meanderingpassage fluidically connected to the second cooling passage section atthe inlet opening and having a cooling inlet opening, the position ofthe passage inlet opening being dependent on a position of the grateblock relative to a grate block following in a direction.
 10. The grateblock as claimed in claim 1, wherein the top wall has a trough-shapedrecess facing the combustion space.
 11. A grate comprising grate blocksas claimed in claim
 1. 12. The grate as claimed in claim 11, comprisinga plurality of fixed grate block rows and a plurality of movable grateblock rows which are arranged alternately, a plurality of grate blocksbeing attached side by side to a grate-retaining tube and being fixedlyconnected to one another and forming the respective grate block rows,wherein both the fixed and the movable grate block rows are formed bythe grate blocks.